Quantum efficiency measurement of an x-ray charge-coupled device by means of an x-ray generator monochromatized over the 0.2-1.2 keV spectral region.

The Atomic Energy Commission has been developing an x-ray calibration laboratory for several years close to the Laser MégaJoule Facility mainly to calibrate x-ray cameras. Based on x-ray generators, great effort is being carried out to obtain x-ray monochromatic sources over the 0.1-10 keV spectral range. Moreover, their routine availability is a prerequisite while getting reduced uncertainties. To achieve this purpose, two x-ray monochromators have been recently developed, the former running below 1.5 keV and the latter in the harder x-ray region. The work presented in this paper constitutes, to the best of our knowledge, the first radiometric calibration of an x-ray camera, namely, a charge-coupled device (CCD). The CCD is thin and back illuminated with a 1300×1340 pixel, 20 µm×20 µm area. It has been calibrated by means of our soft x-ray monochromator based on Rowland circle geometry. This apparatus is able to take on board simultaneously two detectors under vacuum: the CCD to be calibrated and a silicon drift spectrometer (SDD), which acts as a reference detector to obtain the x-ray monochromatic intensity. An internal specific vacuum manipulator allows putting successively each detector in front of the scanning exit slit. Quantum efficiency (QE) of the CCD has thus been measured over the 0.2-1.2 keV region, due to the reference SDD. The latter was previously calibrated on the same monochromator by cross-calibration with another SDD calibrated at the Physikalisch-Technische Bundesanstalt (PTB) Radiometry Laboratory, on the synchrotron radiation facility BESSY. QE measurements are then compared to the CCD manufacturer's model and with previous ones performed on the same camera by means of our hard x-ray monochromator (2-10 keV). Comparison of these results with further PTB efficiency calibration of the reference SDD used to calibrate the CCD is discussed and allows concluding definitively about the validity of measurements performed by our x-ray monochromators.

Process induced transformations during tablet manufacturing: phase transition analysis of caffeine using DSC and low frequency micro-Raman spectroscopy.

The phase transition of a model API, caffeine Form I, was studied during tableting process monitored with an instrumented press. The formulation used had a plastic flow behavior according to the Heckel model in the compression pressure range of 70-170 MPa. The quantitative methods of analysis used were Differential Scanning Calorimetry (DSC) and low frequency Micro Raman Spectroscopy (MRS) which was used for the first time for the mapping of polymorphs in tablets. They brought complementary contributions since MRS is a microscopic spectral analysis with a spatial resolution of 5 µm(3) and DSC takes into account a macroscopic fraction (10mg) of the tablet. Phase transitions were present at the surfaces, borders and center of the tablets. Whatever the pressure applied during the compression process, the transition degree of caffeine Form I toward Form II was almost constant. MRS provided higher transition degrees (50-60%) than DSC (20-35%). MRS revealed that caffeine Form I particles were partially transformed in all parts of the tablets at a microscopic scale. Moreover, tablet surfaces showed local higher transition degree compared to the other parts.

Longitudinal coherence measurements of a transient collisional x-ray laser.

We present what is to our knowledge the first longitudinal coherence measurement of a transient inversion collisional x-ray laser. We investigated the picosecond output of a Ni-like Pd x-ray laser at 14.68 nm generated by the COMET laser facility at the Lawrence Livermore National Laboratory. Interference fringes were generated with a Michelson interferometer setup in which a thin multilayer membrane was used as a beam splitter. We determined the longitudinal coherence for the 4d1S0 --> 4p1P1 lasing transition to be approximately 400 microm (1/e half-width) by changing the length of one interferometer arm and measuring the resultant variation in fringe visibility. The inferred gain-narrowed linewidth of approximately 0.29 pm is a factor of 4 less than previously measured in quasi-steady-state x-ray laser schemes.

X-ray-ultraviolet beam splitters for the Michelson interferometer.

With the aim of realizing a Michelson interferometer working at 13.9 nm, we have developed a symmetrical beam splitter with multilayers deposited on the front and back sides of a silicon nitride membrane. On the basis of the experimental optical properties of the membrane, simulations have been performed to define the multilayer structure that provides the highest reflectivity-transmission product. Optimized Mo-Si multilayers have been successfully deposited on both sides of t he membrane by use of the ion-beam sputtering technique, with a thickness-period reproducibility of 0.1 nm. Measurements by means of synchrotron radiation at 13.9 nm and at an angle of 45 degrees provide a reflectivity of 14.2% and a transmission of 15.2% for a 60% s-polarized light, close to the simulated values. Such a beam splitter has been used for x-ray laser Michelson interferometry at 13.9 nm. The first interferogram is discussed.